Spinneret assemblies for spinning synthetic filaments or fibers typically include an inlet block having an inlet port through which the material to be spun is introduced into the spinneret assembly and a chamber containing filtering material, a distribution plate, a distribution cavity, a metering plate and a spinneret plate. The metering plate includes a number of apertures having a compound shape, consisting of a capillary and a counterbore. The spinneret plate normally includes a corresponding number of bores having a compound shape consisting of a counterbore and a capillary or spinning orifice.
U.S. Pat. No. 3,095,607 to Cobb describes a typical spinneret assembly. Other spinneret assemblies are described in U.S. Pat. No. 3,028,627 to McCormick; U.S. Pat. No. 2,883,261 to McGeorge; U.S. Pat. No. 3,225,383 to Cobb; U.S. Pat. No. 3,289,249 to Nakayama et al.; U.S. Pat. No. 3,601,846 to Hudnall; U.S. Pat. No. 3,659,988 to Walczak; and U.S. Pat. No. 4,738,607 to Nakajima et al.
It is sometimes desirable to change the number of filaments or deniers of the filaments being spun from a single spinneret. Reasons for altering the filament count may include product variations, keeping the total tow denier constant while changing the individual filament denier, changing quenching characteristics and maintaining spinning speed at higher denier per filament where extruder capacity is limited. Also, mixed denier filaments produce unique product characteristics.
The traditional method for changing filament count is to individually plug spinneret capillaries using a soft metal bar of approximately the same diameter as the counterbore. This method is time consuming, risks damage to the spinneret, and does not insure a leak-free seal.
The traditional method of generating mixed deniers is to make expensive, precision metering plates for each mixture.
Another known method for spinning a number of different filament counts from a single spinneret plate is described in U.S. Pat. No. 3,336,633 to Curran. Curran employs metering plates having a number of apertures lower than the number of orifices in the spinneret plate. Since the compound shape of the apertures in the metering plate are normally precision drilled to provide a desired pressure drop, the metering plates are relatively expensive to produce and maintaining a stockpile of metering plates to provide a variety of fiber counts may be cost-prohibitive.
U.S. Pat. No. 2,980,492 to Jamieson et al. describes an apparatus for making mixed denier filaments. The apparatus requires two separate cavities within a single spin pack. Each cavity corresponds to its own portion of the spin pack. This complicated arrangement allows polymer to be fed at two different feed rates, thereby making different denier filaments.